In a healthy shoulder, the proximal humerus is generally ball-shaped, and articulates within a socket, called the glenoid, formed by the scapula to form the shoulder joint. Conventional implant systems for the total replacement of the shoulder joint due to disease or trauma, i.e., a total shoulder arthroplasty, generally replicate the natural anatomy of the shoulder, and typically include a humeral component having a stem which fits within the humeral canal, and an articulating head which articulates within the socket of a glenoid component implanted within the glenoid of the scapula. An implant system for the replacement of only the humeral component of the shoulder joint, i.e., a hemi shoulder arthroplasty, typically includes only a humeral component which articulates within the natural glenoid socket of the scapula.
In addition, “reverse” type implant systems have been developed in which the conventional ball-and-socket configuration that replicates the natural anatomy of the shoulder is reversed, such that a concave recessed articulating component is provided at the proximal end of the humeral component that articulates against a convex portion of the glenoid component. Such reverse shoulder implant systems are thought to provide an increased range of motion for treatment of glenohumeral arthritis associated with irreparable rotator cuff damage, for example, by moving the center of rotation between the humeral component and the glenoid component to allow the deltoid muscles to exert a greater lever arm on the humerus.